Laboratory and clinical investigations will be done on the two arginase genes and enzymes in man and in hyperargininemia due to an inherited deficiency of the predominant arginase in liver, in human subjects. Three patients with arginase deficiency will be studied on a normal diet, on an essential amino acid diet, on sodium benzoate and sodium phenylacetate supplementation and on enzyme replacement with purified human liver arginase in an enzyme reactor. We will assess the intracellular and extracellular amino acid and organic acid pools, urinary waste nitrogen pools and the incorporation of (15N) ammonia into amino acids and urea to determine the degree of biochemical improvement brought about by each therapy. Human kidney-type arginase will be purified to homogeneity and its structural features and subcellular localization compared with that of the liver-type. The expression and control of the two arginase loci in human cells in culture will be studied. Efforts will be made to induce the expression of arginase in a tissue culture cell line (C6) that does not normally express it. The mechanism of the response will be assessed in a cell-free protein synthesis system measuring the translation of messenger RNA. Human liver arginase cDNA made from liver mRNA will be cloned in E. coli using recombinant DNA techniques. The cDNA will be used to promote translation of a large amount of human liver arginase in E. coli for isolation and use in enzyme replacement therapy. Using this probe, the liver and kidney arginase genes in a lambda phage library of human DNA will be cloned and used to determine the number, chromosomal location and base sequence of the arginase genes in man, and will be used to transfect mammalian cell and organ cultures in order to study the stability, expression and control of the gene, as a model for gene replacement.